<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html{
            background-color: gold;
            font-size:50px;
            text-align: center;
        }
        /* 竖屏*/
        @media screen and (orientation: portrait) {
            .tip{display: none;}
        }

        /* 横屏 */
        @media (orientation: landscape) {
            .tip{display: block;}
        }

    </style>
</head>

<body>
    <!-- 提示 -->
    <div class="tip">请把手机转到竖屏的状态！</div>
</body>
</html>